n-factor of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ in acidic medium is (X), n- factor of ${\mathrm{C}}_2{\mathrm{O}}_4^{-2}$ is (Y) and in neutral medium n - factor of KMnO₄ is (Z). Correct relation between them is